Fun idea!

Building on that: there's a common children's magic trick involving a flip book that magically "colors" its pages (https://www.magicinc.net/products/fun-magic-coloring-book?va...)

It works by moving your thumb to a different position while flipping the pages -- every Xth page is cut at slightly different lengths, so when you move your thumb to the next position, different pages become visible during the flip

Using this trick you could show multiple different video clips in the flipbook just by moving your thumb to a different spot

I love that magic trick, but wouldn't that significantly thicken the cardstock flipbook ?

would it? I assume the trick is the sheets are slightly trapezoidal. Shouldn't that be enough?

Of course you're doubling the page count regardless of the approach ... that's likely unavoidable.

This sounds like a Svengali deck, which just has every other card slightly shorter. Then when you flip from one direction it seems like all of the cards are different, and from the other direction, all of the cards appear the same. Would be easy to do, but in one direction your hand would tend to block the view of the cards.